The key to more effective collection is the automated, single-operator packer, which has been in widespread use operating effectively since the early 1980s. In 1982, for example, the city of Sacramento, Calif., conducted a trial program, switching from “curbside-manual, unlimited, combined refuse collection service” to “curbside-automated, 90-gallon container, combined refuse service.” Even though the automated packers of that era were not nearly as effective as today’s models, the city found that the automated approach reduced required collection man-hours by 45.5%, required vehicle hours by 18.5% and total annual costs (including amortized capital costs) by 10.6%.

Similar pilot tests in both large and small municipalities such as Newport News, Va., Warner Robins, Ga., Greensboro N.C., and Pensacola, Fla., have helped put forth a solid case that the automated side-loaders were the most effective way to collect refuse on most routes. Manufacturers kept improving their packers and making them more maintainable and cost-effective. The next logical development was to apply automated side-loaders to curbside collection of single-bin mixed recyclables.

Automating Curbside Collection of Recyclables

The logic for this application was very persuasive. Since the chore of source separation on the part of residents was sharply reduced, it was very likely that this approach would increase participation and recycling rates. Moreover, since most municipalities already had automated side-loaders in their fleet for yard waste and/or refuse collection, a municipality could standardize on the one truck design, with obvious advantages in maintenance, training and overall deployment flexibility. Further, truck payload capacity could be optimized as compared to manual-collection split trucks. The routes could be longer, and the number of trips to a MRF with partially filled compartments would be minimized. And, of course, the single-operator staffing of the automated side-loaders should reduce staffing requirements and increase operator safety.

While these theoretical advantages were enticing, the question remained whether the operating cost savings would offset the higher capital costs of the automated equipment and the 90-gallon barrels that would be needed. In 1996, the city of Los Angeles decided to find out by initiating a major pilot program of collection from more than 4,000 residences on normal routes. The automated packers and two other alternatives were being evaluated as part of a “Second Generation Recycling Program” to replace the city’s existing “yellow bin system.” In this quasi-commingled system, residents placed recyclables other than paper in open 20-gallon bins and placed paper products in paper bags or bundles beside the bins. Each week (assuming they got there before the scavengers), crews would stop and manually place the paper and commingled recyclable containers in different areas of a non-automated side-loading truck.

 Los Angeles Test Results

From a collection standpoint, the automated side-loader/single bin combination was an outstanding success. As described in the pilot project’s final report, “the average tonnage and pounds per household per week collected for Pilot I routes are 6.85 and 15.79 respectively (an increase of 148% from the yellow bin program). The average set-out rate for the five routes in Pilot I is 451 homes/week . . . up 82% from the yellow bin rate in the same areas.”

Encouraged by these results, Los Angeles has implemented this curbside collection system city-wide, serving 720,000 residents. And the operational results have corroborated those of the pilot tests. According to Daniel Hackney of the Los Angeles Bureau of Sanitation, city-wide collection of recyclables had increased by 140% this summer, and each month there continues to be a further increase over the same month in 1998; in August, that increase was 28.8%. And by that time, the city’s diversion rate had reached 44.1%.

“We will achieve our 50% diversion goals by year end,” he asserted, “and we have cut our collection costs by 25% despite recycling 140% more than we did before. We’ve enlarged our routes from 700 to 1,100 homes. And the trucks no longer go to the MRFs only partially loaded. Operationally, we realized savings from avoided landfill tipping charges, from flexibility and maintenance economies from our fleet commonality, and from labor savings achieved through attrition as the more efficient operations that allow us to eliminate surplus positions. Moreover, from a capital cost standpoint, our only major cost has been the $30 million we spent on the 90-gallon containers we supplied to the residents. We were able to switch from recycling trucks to automated sideloaders on our normal truck replacement cycle.”

The Impact on Separation at the MRF

The use of single-bin collection, however, complicates the separation of the recyclables at the MRF. For a typical manual MRF sorting system—perhaps augmented by magnets and an eddy current system—the switch from dual stream to single stream feedstock requires a significant increase in the number of pickers and/or a lower throughput. In the case of at least one MRF contractor in Los Angeles, the per-ton cost of sorting and processing went up drastically.

This resulted in lower offsetting revenues for the city. Operators of five MRFs throughout the city process and market the recyclables and pay per-ton rates to the city as part of their contracts. Different per-ton rates are paid for (1) separated paper, (2) mixed commingled containers, and (3) single stream recyclables. A typical contract entitles the city to $48.50 per ton for separated paper, $124 per ton for mixed commingled containers, but just $26 per ton for single stream recyclables. Thus, the city faces a significant offset to the savings achieved through the improvements to its collection system.

It is this type of economic offset that has deterred many municipalities from implementing single-bin curbside collection of recyclables. Most MRF operators are used to dealing with separated fiber/container feedstock, and have developed high productivity levels in separating commingled materials. They are concerned with the high (typically 15%) contamination of non-recyclables likely with single stream collection and fear that their costs and/or throughput will suffer. Also, they knew that paper mills did not believe that their quality requirements could be met with single stream processing; they were afraid that the paper would be contaminated with glass shards and other residue. Until recently, the technology needed for cost-effective, high throughput sorting systems that produce readily marketable commodities simply had not been available.

 Single Stream Processing Systems

The first plant that combined fiber and containers and processed them using a single stream system was designed and installed in Phoenix in 1991. Using European technology, this was a first class facility with unique automated separation components. The facility was far ahead of its time and was very well run, but it suffered from a major drawback. Operating on the principle of negative sorting of #8 newsprint, the system separated the fibers from the containers at an early stage but kept the mixed paper in with the ONP. Since the Phoenix curbside collection contained about 25% mixed paper, it was a major separation task to remove enough mixed paper to produce #8 newsprint. Since the flat-deck shakers of the system could not effectively sort out this contamination, the separation has had to be done manually. This manual separation has cut the throughput of the $5 million facility to 15 tons per hour and reduced the productivity to 1/3-ton per hour per person.

This productivity was too low for private companies to cost-justify a single stream separation system, with the result that seven years would pass before a second single stream system was sold. During this period, our firm, like most U.S. manufacturers, analyzed the design requirements, but could not devise a less expensive and more effective alternative. Finally, the innovative ideas of our West Coast sales manager led our firm to take a different approach. He proved that if we could focus on initially separating the larger ONP, we could not only produce a very clean #8 newsprint, but we could also double the throughput and triple the productivity. Since by weight, about 50% of a typical curbside load of single-bin recyclables is newsprint, removing it (and OCC) at the outset more than halves the material load on subsequent separation equipment and increases throughput accordingly. All we had to do was find a way to cost-effectively perform that initial sort of the ONP.

Ironically, the key to this improvement was a device we already had developed and had been using in our potato cleaning machines. This star screen is made of rubber discs to which the fiber will adhere much better than to metal. We found that we could mechanize these discs in a screen mounted at a steep incline angle and operating at high speed. Through this action, the newspaper automatically passes over the starscreen. Gravity causes the containers to drop off, and the spacing of the discs in the starscreen allows the mixed paper to drop through.

We first introduced starscreen technology into other recycling equipment in 1994 to facilitate the automatic separation of OCC, ONP, mixed paper, containers and C&D loads. Thus, it was a well-proven technology before we ever applied it to a single stream processing system. Eventually we did apply it to single stream applications, and had our first complete plant in operation in early 1998. Since then, three more plants have been installed, and we have contracted for six additional systems each costing in the $1.5-2.0 million range. Each has a throughput of 20 to 30 tons per hour and a productivity of a ton per man-hour, three times that of the earlier generation Phoenix system. The following paragraphs describe the operation of one of these systems.

Typical System Operation

In a typical single-stream system, a specially designed feeder accepts a big load of incoming material and spreads it through separate belts, speed controls, electronic eyes and load levelers onto a high-speed chain-belt conveyor. This feeds the single stream materials to a primary pre-sorting area where a sorting crew manually removes the large rejects and the cardboard. Seasonal picking of telephone books is optional.

The remaining material is then fed onto two starscreen decks that can be adjusted in such parameters as spacing, individual axle speed, angle of incline and amount of air pressure. (A computer with programmed recipes sets the parameters to adjust for the variations in incoming material, for weather conditions, and/or for the quality requirements of the final product.) The newspaper that the starscreen automatically separates from the rest of the stream is inspected and manually sorted on a quality control line. 

The mixed paper, fines and containers fall back and through the screen onto a special discharge conveyor. This material is then fed onto an adjustable side-angled starscreen called a Single Stream Separator Screen. This unit automatically discharges and bounces the three-dimensional containers down and to the sides. All fiber, such as high-grade paper and junk mail, adheres to the screen and travels over the top end of the side-angled starscreen. This paper is conveyed to the mixed paper sortline where it is manually inspected.

All the smaller pieces of glass, trash, organics, bottle caps and tops, sand and other out-throws fall through the screen and require further processing depending on the quality required by the local glass market. The reprocessing is accomplished by a combination of a screen with a smaller opening to remove the small contaminants, an air knife to remove the paper, and manual picking of larger contaminants.

At this point, at least 80% of the original stream has been diverted, leaving only containers to be separated. Since these containers are of a homogeneous size and are not shielded from separation equipment or pickers, the separation is very fast and effective. First, magnets remove the ferrous materials; then the containers pass over an air knife that sends the light fraction (largely HDPE, PET, and aluminum cans) to an elevated sortline, and allows the heavy glass to proceed to another sortline for manual color separation into different bunkers. On the elevated sortline, eddy current equipment automatically ejects the aluminum. Plastic containers are manually sorted into colors and types.

All of the separated materials are deposited into bunkers positioned below the conveyor lines. When a bunker is full, its material is automatically conveyed to a baler. Depending upon the sophistication desired, a system computer can be programmed to learn when a bunker is about to be full, and cause that bunker’s material to be conveyed to a baler.

Other System Configurations

The system just described presents the required functions and the preferred sequence of these functions, but it should be stressed that each specific system configuration will be shaped by the unique requirements of each MRF and the equipment proposed by the competing suppliers. For example, a municipality that has an unusual amount of glass to be recycled and/or which benefits from a bottle law might want to add a glass separation system to this configuration. Several firms offer such a separator for about $375,000 ($125,000 for each color to be separated). Similarly, there are now electronic separation systems for plastics. Here, the additional cost will be about $400,000 to separate four different products. In order to cost-justify the acquisition of either of these technologies, it would require at least a total input of 400 tons per day of single stream recyclables and a viable local market (or subsidy). Of course, these technologies might well justify their costs as an augmentation for larger plants processing commingled or either glass or plastic as a single commodity.

On the other hand, not all MRFs have the volume that requires a fully automated system that can handle hundreds of tons per shift. A customer who only needs to process perhaps 120 tons per day might well prefer a downsized system that would get him up and running in a shorter period of time and at a substantially reduced cost. Such a system contains most of the basic system functions, and can be expanded to provide full system capability and capacity.

 It may well be, though, that investing in this smaller system would be a false economy. I believe that as soon as a MRF becomes capable of processing single stream recyclables effectively, the sources of supply are very likely to grow rapidly, requiring (and incentivizing) that MRF to operate multiple shifts. Therefore,  MRF operator should specify a single stream system with a higher capacity than its current production mandates.

Almost invariably, such planning for growth pays off. In this instance, bigger is better. As the tonnage capacity goes up, the operating costs go down.  We are looking forward now to systems of tomorrow that may cost $2 million, but will be able to lower operating costs to as low as $25 per ton! For some MRF operators, that will be the most important factor in the separation and recovery of recyclables. And operating costs like that will support, not offset the savings generated by single-bin collection so that more municipalities can cost-effectively increase their recycling volume and meet their diversion goals.

Erik H. Eenkema van Dijk is Executive Vice President of Van Dyk Baler Corp., Stamford, Conn., which supplies Bollegraaf equipment (including balers and turnkey sorting systems). The company is considered an authority on single stream recycling.